VS 2017 Preview installs to a different directory from VS 2017 RTM, so
the packaging script needs to be updated to handle this. It does this by
using vswhere.exe so that any VS 2017 install can be found
automatically. If there are multiple installs then it is not well
defined which one will be found, so make sure you don't have multiple
installs.

The other change is to more robustly find the many directory paths which
contain embedded version numbers. Previously these were hard-coded for
VS 2017 RTM but this quickly gets tedious so now glob.glob is used to
find the matching directories. This will intentionally fail if there is
any ambiguity.

R=scottmg@chromium.org
BUG=683729

Change-Id: I02f7ae7589e271d6d9897f899e0730d7163f76ef
Reviewed-on: https://chromium-review.googlesource.com/516442
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>